1. Field of the Invention
This invention relates to integrated circuits capable of operation in the microwave range and, more specifically, to such integrated circuits fabricated in silicon technology and methods of fabrication thereof.
2. Brief Description of the Prior Art
Integrated circuits capable of operation in the microwave range are finding increasing use, primarily in consumer and commercial applications, such as, for example, mobile communication. Prior art integrated circuits capable of operation in the microwave range have generally been fabricated using gallium arsenide substrates and possibly other group III-V semiconductor technologies. Gallium arsenide substrates have been generally preferred because of their intrinsic device performance, good isolation properties between devices at microwave frequencies due to the high resistivity of intrinsic GaAs substrates and the low loss transmission line interconnects formed as a result of the low dielectric loss of high resistivity GaAs substrates.
Particular problems associated with group III-V substrates and particularly gallium arsenide substrates are their high starting cost, the low yields obtained compared with silicon technology. The result is that semiconductor devices such as integrated circuits fabricated in group III-V technologies and particularly gallium arsenide are high cost devices relative to silicon technologies.
Furthermore, in order to provide a transmission line interconnect, it is necessary to provide a dielectric of very low loss which must also be relatively thick, for example 50 to 100 micrometers. In group III-V technology, the dielectric has generally been an "air bridge" wherein air is the dielectric or an intrinsic GaAs substrate which has very high resistivity relative to silicon.